Land-use impacts on river water quality in lowveld sand river systems in south-east Zimbabwe

We examined spatial patterns of physico-chemico characteristics and nutrients of freshwater lotic systems in impaired waters in sand river systems in a semi-arid tropical lowveld region of south-east Zimbabwe, from August 2003 to April 2004. These changes were viewed in the context effluent discharge and land use. The high concentrations of dissolved compounds in the Runde River shows that the chemical composition of this river water is determined largely by the inflowing waters from surrounding irrigated lands. The elevated levels in nutrients recorded along the Runde River suggest that agricultural activities are a key determinant of ecosystem structure and function, especially of algal and invertebrate biomass and productivity in the south-east river systems. This study also shows that nutrient eutrophication of lotic systems may have indirect beneficial impacts on the fish population through increased fish food supply. Lotic ecosystems should be viewed as being influenced profoundly by agricultural activities.